The present invention relates to the preparation of whiteware ceramic articles by pressing.
It is known that various whiteware ceramic articles may be prepared by pressing. Examples of different types of pressing techniques include uniaxial pressing, isostatic pressing, dry pressing, hot uniaxial pressing, hot isostatic pressing and hot dry pressing.
Dry pressing is an example of a well-known pressing technique by which ceramic articles are prepared. In dry pressing, a particulate material is suspended in a slurry medium, generally with other additives selected to control both the properties of the slurry and the properties of the article ultimately prepared from the slurry. The solvent is removed to prepare a powder having particles of the desired size or range of sizes. This powder is then placed into dies having the desired shape and pressure is applied to form the green ceramic article which undergoes additional processing. The pressure involved in dry pressing is applied either unilaterally as in dry pressing or from all directions as in isostatic dry pressing. Pressing operations may be carried out at various temperatures including room temperature or elevated temperatures.
While pressing techniques are well-known to those skilled in the art, there are some problems associated with these processes and the articles produced therefrom. A particular example of such problems concerns poor green strength. Attempts have been made to use various additives to correct such problems. For example, it is known to use substances known as binders such as polyglycols to increase the green strength of ceramic articles prepared by pressing. Typically, these binders are added at a level of several percent to result in significantly improved green strength. Unfortunately, the necessity of adding several percent of these additives frequently results in ceramic articles with undesirably altered characteristics.
It is desirable to have an additive for use in the preparation of whiteware articles by pressing which would be effective at low dosages, have low molecular weight, good burnout characteristics, and would result in pressed whiteware articles having good properties such as high green strength.